1. Field of the Invention
The invention pertains to a vibration damper having a cylinder with an inside wall surrounding a working space; a piston rod guide having an outside surface which rests against the inside wall of the cylinder adjacent to the working space, the guide having an internal end surface facing the working space and an external end surface facing away from the working space; and a seal between the outside surface of the piston rod guide and the inside wall of the cylinder.
2. Description of the Related Art
In vibration dampers of the single-tube design, all the components and the working media are installed or added through the open end of the cylinder. In many cases, only the open area near the piston rod guide is available. The piston rod guide has a first groove on the outside diameter for a sealing ring and a second groove, offset axially toward the outer end surface, into which certain parts of the cylinder are lock-beaded to hold the piston rod guide axially in place. During assembly, the vibration damper must be completely filled with oil, which means that the cylinder will contain a certain excess amount of oil. During the installation of the piston rod guide, therefore, a certain amount of this damping medium can make its way into the second groove, especially because of the effect of the installing device, which is wetted with the damping medium. During the lock-beading operation, some of the damping medium present in the second groove is displaced toward the end surface. This excess damping medium can be removed easily from the external surfaces. The damping medium still remaining in the second groove, however, is more critical. During the further course of the assembly process and also at a later time, especially during installation of the vibration damper in the motor vehicle, the damping medium trapped in the second groove can escape through the gap between the cylinder and the piston rod guide and reach the end surface. The purely superficial impression can thus be created that the vibration damper is leaking. Only an inspection in a testing machine can determine whether or not the vibration damper is in fact defective or whether it merely presents the appearance of a defect.
Thought has already been given to the possibility of locating the second groove with the lock-beading near the working space on the piston rod side and the first groove for the seal near the end surface of the vibration damper. It this case, however, it is still possible for very fine cracks to be formed in the cylinder during the lock-beading operation—cracks which can lead afterwards to a leak in the vibration damper.